1. Field of the Invention
The present invention relates to various video scramble systems and equipments embodying these scramble systems for omitting unqualified watchers in a pay television system such as CATV.
2. Description of the Prior Art
In a pay television system such as CATV, scrambling to video signal is being conducted in order to avoid unqualified TV watchers. Hitherto, such comparatively simple systems have been adopted as the gray-sync system in which a synchronizing signal is suppressed using modulation by an encode signal having such phase relation as suppressing a horizontal synchronizing signal, and as the inverted video system in which the modulation polarity of a video signal is inverted to be transmitted.
However, when one of the above mentioned system is used, while low cost decoders are provided, it was easy to manufacture devices for tapping, so that it has been a difficult problem to realize a perfect avoidance of these unqualified watchers.
On the other hand, in the satellite TV broadcasting system or the like, scramble systems having high grade of concealment such as the line permutation system or the line rotation system utilizing digital signal processing are adopted, but it was found out that these scrambling systems were not suitable to CATV system because of the fact that a decoder for these systems could be very expensive due to a complexity of the digital signal processing itself.
The present invention has been accomplished based on the above mentioned situations, and the object of the invention is to provide a new video scramble system and an equipment which is of rather low cost and having high grade of concealment of scramble, yet making it difficult to manufacture tapping equipments for decoding the scramble.